The present invention relates generally to systems and methods for destroying tissue using focused ultrasound, and more particularly to systems and methods for destroying tissue by focusing ultrasound from an external source towards subcutaneous tissues, such as adipose tissue to aid in body contouring.
Liposuction is a commonly used cosmetic surgical procedure for removing fat (adipose) cells to achieve a more desirable body shape. Liposuction usually involves an invasive surgical procedure, which includes penetrating the skin, melting or shearing the adipose tissue, and mechanically removing the adipose tissue using a vacuum or other suctioning device.
Tumescent liposuction is a common variation in which xe2x80x9ctumescentxe2x80x9d solution is introduced into a target tissue region, e.g., a layer of fatty tissue, to loosen the structure of the fatty tissue and to facilitate its suction. The tumescent solution generally includes, among other possible ingredients, a topical anesthetic, such as lidocaine, and a vasoconstrictor to reduce bleeding, such as Norinephrine. Generally, a large quantity of tumescent solution is infiltrated, e.g., in a one-to-one ratio with the fat to be removed, causing the tissue region to swell. Suction is then performed using a special cannula connected to a vacuum system that is introduced into the fatty layer through incisions in the patient""s skin, typically three to six millimeters (3-6 mm) wide. The cannula is moved around inside each incision to reach target sites within the tissue region that are to be removed.
Traditional liposuction, however, is an extremely invasive, possibly traumatic procedure. As the cannula is moved through the tissue region, it may damage nerves and/or blood vessels, as well as the fatty tissue. Thus, complications include excessive bleeding, creating a significant risk of morbidity and/or mortality. Another potential problem with liposuction is lack of uniformity of the patient""s final shape due to irregular removal of the fatty tissue.
In recent years, ultrasound has been suggested for assisting in liposuction procedures. For example, ultrasound assisted liposuction (xe2x80x9cUALxe2x80x9d) involves introducing a solid stick ultrasound transducer through an incision in the patient""s skin and moving the transducer through a fatty tissue region. The transducer emits ultrasonic energy, generally at frequencies of 20-30 kHz, that may heat the tissue in the region until necrosis occurs, and/or may cause cavitation, thereby rupturing adipose cells in the region. Subsequently, a cannula is introduced into the tissue region to perform suction, as described above. Alternatively, a hollow transducer may be used that provides suction simultaneously with the delivery of ultrasonic energy.
One problem associated with known UAL techniques, however, is that the transducer may become quite hot during its use. This may result in damage or destruction of tissues adjacent to the target region by overheating or melting. To protect tissue outside the target region, the transducer may be introduced through the skin using an insulated sleeve, although this may require a much larger incision, e.g., about ten millimeters (10 mm) or more wide. In addition, the doctor may need to use extreme care and keep moving the transducer in order to avoid burning tissue. Finally, treatment may also be limited to direct contact between the transducer and the adipose tissue, possibly resulting in non-uniform destruction of fat cells in the target region.
As an alternative to UAL techniques, U.S. Pat. No. 5,884,631, issued to Silberg, discloses using an external ultrasonic generator to transmit ultrasound waves through a patient""s skin to underlying adipose tissue. Silberg proposes using ultrasonic energy at a frequency above about twenty kilohertz to disrupt the connective tissue between fat cells, whereupon conventional liposuction may be used to remove the cells. The ultrasound energy in Silberg, however, is not focused, but instead is delivered from a point contact on the surface of a patient""s skin indiscriminately into the underlying tissue. Such unfocused ultrasonic energy may be ineffective for facilitating liposuction since the energy is merely diffused generally into the underlying tissue.
In addition, noninvasive methods have been proposed for removing adipose tissue. For example, U.S. Pat. No. 5,143,063, issued to Fellner, discloses a device and method for necrosing adipose tissue by directing radiant energy directly to a tissue region or work site. Although Fellner generally discloses the use of radiant energy, such as radio frequency, microwave, or ultrasonic energy, the only specific examples given for focusing ultrasonic energy at a subcutaneous tissue region involve using a concave lens or a Barone reflector. Such a lens or reflector, however, may have a fixed xe2x80x9cfocal distance,xe2x80x9d i.e., the distance from the device to the xe2x80x9cfocal zone,xe2x80x9d i.e., the region to which the energy is focused. In addition, such devices may only generate a relatively small focal zone having a fixed size and shape.
In addition, the exemplary procedure suggested by Fellner involves focusing energy at a work site for at least about thirty to forty minutes in order to effectively heat and necrose tissue at the work site. Thus, the suggested procedures may be time-consuming and/or may risk heating or damaging tissue outside the work site.
Accordingly, systems and methods for destroying subcutaneous tissue and/or for providing more precise monitoring and/or guidance of focused ultrasonic energy used to remove adipose cells or other tissue would be considered useful.
The present invention relates generally to systems and methods for focusing ultrasound energy from a location external to a patient to rupture or otherwise remove cells, such as adipose cells, within a subcutaneous tissue region. The present invention may minimize damage, such as that caused by invasive surgical procedures and/or by heating of neighboring tissues when unfocused ultrasound is indiscriminately introduced into a tissue region. The target cells, preferably adipose cells, may be ruptured and then removed, for example, by natural excretion mechanisms within the body or by gentle suction.
In a preferred method, a transducer is disposed externally adjacent to the patient""s skin. The transducer is driven with drive signals such that the transducer emits acoustic energy, while the acoustic energy is focused at a focal zone within a target tissue region. The acoustic energy, preferably ultrasonic energy, has sufficient intensity to cavitate fluid within the focal zone, thereby rupturing or otherwise destroying tissue, e.g., adipose cells, within the focal zone. The ultrasonic energy is preferably applied using a relatively low duty cycle, i.e., in short bursts relative to the time between successive bursts to limit the amount of heating of tissue in and around the target tissue region. For example, the transducer may be operated using a duty cycle of about twenty percent (20%) or less, preferably about ten percent (10%) or less, and more preferably about one percent (1%) or less. Preferably, the transducer may emit ultrasonic energy at a frequency range between about two and ten megahertz (2-10 MHz), and more preferably between about four and six megahertz (4-6 MHz).
Various embodiments are contemplated for a transducer in accordance with the present invention. The transducer may have either a fixed focal distance or a variable focal distance. xe2x80x9cFocal distancexe2x80x9d is the distance from an acoustic emission surface of the transducer to a center of the xe2x80x9cfocal zone,xe2x80x9d i.e., the region where energy from the transducer is focused. In a preferred embodiment, the transducer is preferably configured for producing a substantially linear focal zone. The transducer may have a single transducer element, thereby having a fixed focal distance. For example, a single partial cylindrical transducer may be provided that focuses ultrasonic energy due to its geometry, or a substantially planar transducer may be provided that includes a lens for focusing the ultrasonic energy at a desired focal zone.
Alternatively, the transducer may include a phased array. For example, the transducer may include a plurality of linear transducer elements disposed adjacent to one another, e.g., in a partial cylindrical arrangement or in a substantially planar arrangement. Alternatively, the transducer may include a plurality of transducer elements defining respective portions of a single arc, each of which is projected onto a plane. Thus, the plurality of transducer elements may be arranged in a configuration similar to a Fresnel lens. Such a transducer configuration may substantially minimize the space between the acoustic emission surface of the transducer and the patient""s skin, facilitating acoustically coupling the transducer to the patient and/or minimizing air gaps between the transducer and the patient""s skin.
Drive circuitry is coupled to each individual transducer element, the drive circuitry being controlled by a controller. Drive signals from the drive circuitry cause the transducer element(s) to emit ultrasonic energy. The controller may control a phase shift value of respective drive signals to the transducer elements, thereby adjusting a focal distance to the focal zone.
In yet further embodiments, a transducer array may be provided that generates multiple simultaneous focal zones. These systems may include a plurality of individual transducers that are disposed side-by-side in a substantially planar configuration, thereby being capable of generating a plurality of substantially parallel linear focal zones. Treatment time may be decreased with such a multiple-focal zone embodiment, as will be appreciated by those skilled in the art.
In accordance with another aspect of the present invention, a transducer may be provided that includes one or more detectors for measuring ultrasound signals produced during cavitation. Generally, cavitating gas bubbles produce a strong signal, for example, at a frequency of approximately one half of the transmitted ultrasound waves. An acoustic sensor, such as a cavitation strip detector, may be provided on the transducer for detecting such cavitation signals.
A monitoring system may be coupled to the detector for monitoring cavitation during a procedure. For example, the system may include a processor that correlates the cavitation signals to determine the extent of cavitation, and consequently tissue destruction, occurring in the target tissue region. Preferably, a rate of change in amplitude of the detected signals may be monitored to determine when cells within a target tissue region have been substantially destroyed. Alternatively, the amplitude of the cavitation signals may be integrated over time until a predetermined value is reached. In addition or alternatively, the system may monitor the cavitation signals to ensure that a predetermined peak amplitude, i.e., rate of cavitation, is not exceeded, e.g., to provide a desired safety factor against excessive cavitation, which may be harmful to the patient.
Additionally, in accordance with another aspect of the present invention, an apparatus may be provided for moving an ultrasound transducer (or a set of transducers) in a controlled manner. For example, the transducer may be mounted to a frame that may be disposed adjacent the patient""s skin. The transducer may be moved along the patient""s skin, e.g., continuously or incrementally, to cavitate successively adjacent tissue regions, thereby providing a more uniform treatment.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.